1. Field of the Invention
This invention pertains to the field of multifunctional ligands, colloidal nanoparticles and colloidal bioconjugates.
2. Description of Related Prior Art
Known methods to prepare water-soluble nanoparticles, such as demiconductor nanoparticles (quantum dots) and matallic nanoparticles, involve the capping of those nanoparticles with ionized dihydrolipoic acid molecules. Electrostatic self-assembly techniques allow one to easily prepare bioconjugates that take advantage of positively charged domains of proteins coupled to the negatively charged carboxylate groups on the nanoparticle surface. Some limitations to this approach include the restriction of operating in basic environments and the inability to form direct covalently linked nanocrystal-biomolecule conjugates.
Other known approaches have used small organic surface ligands, such as mercaptoacetic acid and aminoethane thiol, to generate water-soluble nanoparticles and other systems. The major disadvantage of such systems involves the poor temporal stability of the nanoparticle ligands due to the nature of the singly bound water-solubilizing groups which results in aggregated solutions after a short time. Water solubilization of nanoparticles with hydrophilic dendritic structures and layer-by-layer assembly techniques has also been demonstrated with some degree of success. Most of these strategies provide for any pH stability, let alone long-term water solubility.